Amplitude filter



Dec. 31, 1940. SCHLESINGER 2,226,994

AMPLITUDE FILTER Filed April 24, 1955 nven for Patented Dec. 31, 194.

UNlTED STATES PATENT OFFICE 2,226,994 AMPLITUDE FILTER 1 KurtSchlesinger, Berlin, Germany, assignor, by

mesne assignments, to Loewe Radio, Ines a corporation of New YorkApplication April 24, 1935, Serial No. 17,960

In Germany April 28, 1934 2Claims. (Cl. 178-7.3)

1 of amplification of this signal, in which the relative amplitudes ofthe impulses remain unaltered, whilst the absolute values are greatlyvaried, of shifting the threshold value so that, as before,

only the. extreme peaks of the. signal pass the filter, Whilst theamplified signals of lower amplitud-es, as before, are withheld.

Forthis purpose, according to th invention, there are provided in thecircuit means which cause the separating. value of the mixture to be bevaried corresponding with. the variations in the total amplification.

Thesemeans may be constructed as automatically acting or also asmanually controlled means. The arrangement according to the invention isof particular importance as regards television receivers, which are tobe synchronised from the transmitter andmakes use of a three-electrodevalve in connection with a grid leak resistance with a parallelconnected capacity. l

The method according to the invention is described in conjunction withthe drawing, where in; g V

Figure 1 shows one form of the present invention and Figure 2 showscomparative signaling strengths of the detected signals.

From a receiving rectifier l, in Fig. L'for example a push-pulldetector, the image current passes over a line 2 through the medium of aa condenser 3 to the Braun tube 4.,,The line 2 is accordingly traversedby image potentials of the order of for example, approximately :10volts. In Fig. 2 the amplitude values for strong and weak reception areshown the values for weak reception being shaded or hatched. Thus, for

' example, for a strong received signal theextreme white is entered with+10 volts, and the extreme black with 10 volts. With a ratio as 3:2between the amplitudes of synchronisation impulses and. maximum imagecurrents the peaks of the synchronizing impulses in Fig. 2 then have anamplitude of 15 volts.

The shaded values apply to weak reception. They are given as :3 voltsfor the imag and p -4 volts for thesynchronlsationsignals. The

object of the circuit according to the invention consists in performingan amplitude filtering for example at either of the values -12 or -3.5,and in allowing all impulses to pass which are more negative than thstated value and withholding the remainder. The desiredlimits are 5shown in dash-dotted lines in Fig. 2 and are designated 6 and 6'respectively.

The problem is solved according to the invention for example by asingle-grid tube 1 in Fig. 1 in the following manner: The cathode of thetube 1 is connected through a resistance 8 of approximately 0.1 megohmwith a positive potention of 3.5 volts as compared with the'grid 9 ofthe same tube. At the same time it is connected with the line 2'traversed by the image current through a condenser 3" of approximately0.005 mf, which blocks the passage of low frequencies, but 'allows thepassage of the short and long synchronisation impulses to-an equaldegree. The potential of the anode battery I0 is selected to be suchthat the anode current only commences when the potential cathode andgrid exceeds the blocking value of 3.5 volts. It is clear thatimmediately the cathode receives negative impulses greater than thismagnitude from the image current line 2, the extent ofwhich exceeds thestated value, corresponding current impulses will occur in the anodecircuit. These current impulses have in themselves a negative sign; theyshould, therefore, as already set forth by the applicant on a previousoccasion, preferably be reversed in their phase by means of two flatlytuned transformers H and [2. The transformer is tuned to the frequencyof the short and the transformer l2 to the frequency of the longsynchro- 5 nizing signals. With the terminals l3 or l4 there may then bedirectly connected the control grids of the relaxation oscillators,which preferably contain a gas discharge tube.

vIf the signals in the line 2 become stronger owing to a higher degreeof amplification by the receiver or by increase in the intensity of thereceiving field or the like, there would be, if special precautions werenot taken, not only an overcreasing the cut oil? level 6' in Fig. 2 to acorrespondingly greater value 6, i. e., for example from 3.5 to 12volts, is solved according to the invention by utilising the gridcurrent in the tube 1. For this purpose the grid is earthed through acondenser l5 and a parallel resistance It. The

condenser 15 is selected to be so small that it short-circuits the highfrequencies, but on the other hand it may be charged in a comparativelyshort time by the grid current (a suitable value is e. g., approximately100 mmf.). If the leak resistance I6 were missing, the grid, therefore,would apparently be charged to the highest negative peak valueoccurring, A control effect in the anode circuit would, therefore, ceasealtogether. By reason now of the leak resistance It the grid is chargednot to the peak value of the maximum negative potential, but to a valuethat is always less negative to a certain extent.

In consequence only the extreme peaks of the impulses-and onlytheseappear in the anode current. The resistance I6 is so selected thatthe condenser I 5 is only capable of again being group of lines, and notbetween every line. The sameQtherefore, in View of the small value [5,must have an appreciably high value of several megohms. As a result onlyvery small amountsof current are necessary for maintainingthe bias valueof the grid once it is adjusted.

. -The"problem of subsequently regulating the amplitude sensation levelin accordance with the output potential in the line 2 may be solved notonly in the stated manner, but also in other fashion. I

It is possible, for example, according to a modification of theinvention, to obtain the bias for the grid of the tube 1 from apotentiometer, and couple this potentiometer mechanicallywith theamplification control, so, that the bias is adjusted so that thesynchronizing signal is separated even with the weakest reception. Thebias then becomes more negative when stronger signals are received andthe separation level is changed to effect the desired results.

According to the invention, there is also the possibility of conductinga part of all of the bias of the grid 9, over a line H and a high-passfilter consisting of the resistance It and the condenser IE! to thecontrol grids of one or more receiving amplifier valves of thetelevision receiver so that the output potential of theline 2 ismaintained constant automatically. r

The method which has been described above for upwardly modulatedtelevision transmitters and negatively poled synchronizing signals maybe employed also for other kinds of modulation, For exampletransmissions with positively poled impulse'peaks may also be receivedby interchanging the cathode and grid connections, i. e., the condenser3 is connected with the grid 9 instead of with the cathode.

In the case of possible capacitative coupling of the grid circuit andanode circuit there may also be introduced in obvious fashion a screengrid. An important advantage may be obtained by utilizing thecurvatureof the characteristic of the amplifier to obtain a considerableincrease in the amplification of the synchronizing signals as comparedwith the image current signals, so that danger of interference with thesynchronizing by peaks in the image current is lessened to aconsiderable extent.

I claim: I p

1. A television receiver wherein picture and synchronizingsignals arereceived as a modulation of a common carrier frequency and wherein thesynchronizing signals have a greater amplitude than any picture signals,means for amplify-' ing the modulated carrier frequency, a demodulatortube having input and output electrodes,

connected condenser and resistance combination for connecting thecontrol electrode of said separator tube to the negative terminal of thesource of potential, means including a load circuit for connecting theoutput electrode of said separator tube to'the positive terminal of thesource of potential, means including an impedance for normallymaintaining a positive bias on the cathode v relative to the controlelectrode by a predetercharged after termination of a relatively largemined amount, means including a condenser for connecting the cathode ofsaid separator tube to the output electrode of said demodulator tube tovary the potentialof said cathode in accordance with, variations inamplitude and voltage of the detected picture and synchronizing signalsfrom a predetermined normal amplitude and voltage Value, said resistanceand condenser combination being adapted to alter the bias voltageapplied to the control electrode of the separator tube in a negativedirection in accordance with increases in the signal strength of thedetected synchronizing signals; whereby said separator tube is ren--dered conductive only upon the presence of synchronizing signalsirrespective of the variations in the amplitude and voltage of thedetected signals, andconductive means for coupling the control electrodeof the separator tube to the means for amplifying the modulated carrierfrequency to vary the amplification level thereof.

2; A television receiver wherein picture and synchronizing signals arereceived as a modulation of a common carrier frequency and wherein thesynchronizing signals have a greater amplitude than any picture signals,means for amplifying the modulated carrier frequency, a demodulatortubeihaving input and output electrodes, means forapplying the modulatedcarrier to the input electrode of the demodulator tube whereby detectedpicture and synchronizing signals are present at the output electrode ofsaid tube with the synchronizing signals extending in a negativedirection, a separator tube including a cathode, a control electrode andan output electrode, a source of potential, means including a parallelconnected condenser and resistance combination for connecting thecontrol electrode of said separator tube to the negative terminal of thesource of potential, means including a load circuit for connecting theoutput electrode of said separator tube to the positive terminal of thesource of potential,means including an impedance fornormally'maintaining a positive bias on the cathode relative-to thecontrol. electrode by a predetermined amount, means including acondenser for connecting the cathode of said separator tube to theoutput elect-rodeof 'said demodulator to vary thepotenti-al of saidcathode in accordance with variations in; amplitude and voltage of thedetected pictureand synchronizingsignals from a predeterminednormalamplitude and voltage value, said resistance and condensercombination being adapted to alter the bias voltage applied to thecontrol electrode of the separator tube in a negative direction inaccordance with increases in the sign-al strength of the detectedsynchronizing sign-alswhereby said separator tube is rendered conductiveonly upon the presence of synchronizing signals irrespective of thevariations pling the control electrode of the sepai'ator tube in theamplitude and voltage of the detected sigto the means for amplifying themodulated carnals, the time constant of said condenser and rierfrequency to vary the amplification level resistor combinationcorresponding to the time thereof.

interval occupied by several successive synchro- KURT SCHLESINGER. 5 nizing signals, and conductive means for cou-

